Movable venturi type tube flow meter

ABSTRACT

A flow meter for measuring the rate of flow of a liquid regardless of the viscosity losses. The flow meter includes an axially movable Venturi tube arranged between a pair of stationary tubes coaxial with the Venturi tube and respectively feeding liquid to be measured in and out of the Venturi tube, first actuator means connected to the Venturi tube for movement therewith in axial direction during flow of liquid through the latter, second actuator means actuated by the pressure in the liquid at the inlet and outlet end of the Venturi tube, and means for determining the actual flow of liquid through the Venturi tube, which means is actuated by the first and second actuator means.

United States Patent Shiba [451 Sept. 26, 1972 [54] MOVABLE VENTURI TYPETUBE FLOW METER [72] Inventor: Kamekichi Shiba, No. 159,

[63] Continuation-impart of Ser. No. 743,200, July 8, 1968, which is acontinuation-in-part of Ser. No. 500,666, Oct. 22, 1965, Pat. ,No.

2,987,915 6/1961 Hildenbrandt ..73/21 1 2,995,933 8/1961 Patton ..73/2133,104,549 9/1963 Humbert et al ..73/228 3,333,468 8/1967 Jacobs ..73/1943,374,674 3/ 1 968 Schwartzman ..73/213 Primary Examiner-James J. GillAttorney-Michael S. Striker [57] ABSTRACT A flow meter for measuring therate of flow of a liquid regardless of the viscosity losses. The flowmeter in- 3429J81- cludes an axially movable Venturi tube arrangedbetween a pair of stationary tubes coaxial with the UQSI Cl.undone-73,194 M Venturi and feeding to be [51] Int. Cl "Golf l/00measured in and out of the Venturi tube fi actuator [58] Fleld ofsearchmnl 194 9 means connected to the Venturi tube for movement 73/213228 therewith in axial direction during flow of liquid f through thelatter, second actuator means actuated by [56] Re erences cued thepressure in the liquid at the inlet and outlet end of UNITED STATESPATENTS the Venturi tube, and means for determining the actual flow ofliquid through the Venturi tube, which 2,364,930 12/1944 Turner ..252/52means is actuated by the first and second actuator 2,538,785 1/1951Karig ..70/119 means 2,804,771 9/1957 Brown .....73/228 2,975,635 3/1961Kindler ..73/194 14 Claims, 9 Drawing Figures 6 4 7 (4 g? 1 l I 00w gywl' 8) r- /4- /A) a (B) A l I a L I 010, 1Q -12 sum 1 or 3 ATENTEDSEPZBI972 F I G.

INVENTOR KAhElucm 9/619 ATTORNEY FIGB PATENTEDSEP26|972 3,693,437

sum 2 [If 3 FIG.4

INVENTOR KAflEkIcm 5/1184 771.110 fffw ATTORNEY lA'TENTEnsir zs I972SHEH 3 BF 3 FIG.7

TRANSD l A 15 6 UcER L Qflff/j/Z/CA T0R FLOW INDICATOR COMPUTERTRANSDUCER IND/CA T0R Q COMPUTER FLOW INDICATOR LAP IND/CA T0R J [AP/ND/CAT0R I TRANSDUCER [TRANSDUCER l fi i J5 W TRANSDUCER FLOW IND/CATQQ INVENTOR. kuwmun $0184 MOVABLE VENTURI TYPE TUBE FLOW METER CROSSREFERENCE TO RELATED APPLICATIONS The present application is acontinuation-in-part Application of the copending application Ser. No.743,200, filed July 8, 1968, which in turn is a continuation-in-partApplication of the application Ser. No. 500,666, filed Oct. 22, 1965 andnow US. Pat. No. 3,429,181.

BACKGROUND OF THE INVENTION This invention relates to a movable Venturitype tube flow meter.

Conventional flow meters in which the flow rate of fluid passing througha conduit is obtained by measur ing its pressure and the like, aremostly based on Bernouillis theorem. However, said theorem is based onthe law of conservation of energy so far as said energy is mechanical,and it is not applicable in every instance, i.e., it is inapplicable incases in which the viscosity of the fluid is not negligible.

The movable Venture type tube flow meter of the present invention is ahydrodynamical flow meter which is not based on Bernouillis theorem, andhence it enables the measurement of a flowrate in every instance, thatis, even in an instance where Bemoillis theorem is not applicable.

Though the law of conservation of energy generally holds true in allcases when all kinds of energies are taken into account, said law doesnot hold true when the energies are limited to mechanical energy as inthe case of proving the Bernouillis theorem and especially when thermalenergy and the like is additionally related to. Therefore, in the casewhen the viscosity of fluid cannot be ignored, Bernouillitheorem isinapplicable.

Whereas, the law of conservation of momentum based on the law of motion,that is, the increase of momentum of a particle in an infinitesimal timedt is equal to dz times as great as the resultant of the external forcesexerted on the particle holds true in every instance within the limitsof Newtons dynamics. The present invention is based on this law.

It is to be noted that the terms flow of fluid herein after used areconsidered to imply incompressible fluid of steady flow.

The working hypothesis of the flow meter according to the presentinvention will be explained hereinafter in detail.

The present flow meter comprises a pair of fixed and coaxial inlet andoutlet tubes spaced from each other in axial direction, and a coaxialVenturi type tube movably connected to said inlet and outlet tubes byresilient means or elastic joints.

(1) The forces exerted on the fluid in the movable Venturi type tube arethe force DA and DB given by the pressure onto the fluid at the inletopening and outlet opening of the Venturi type tube, and the force f bythe Venturi type tube and the gravity thereof. Said force DA and @B canbe expressed by the following equations in which 8,, and 5,, representthe sectional areas of the inlet opening A and outlet opening B of theVenturi type tube, Pand P the pressure working thereon, and thedirection of flow is expressed in a positive sign.

The gravity acting on the fluid in the Venturi type tube can beexpressed by Vpg' in which V represents the capacity of the movableVenturi tube, p the density of the fluid, pg' the component ofacceleration of gravity in the flow direction.

Hence, the forces exerting on the fluid in the Venturi type tube areexpressed as follows:

(2) The increase of momentum which the fluid within the tube obtains inan infinitesimal time dt is discussed hereinafter. It is observed thatthere is no change in momentum of the fluid while it is within theVenturi type tube, because in the tube the fluid forms a steady flowwhere the fluid is constantly replaced with replenished fluid. Whereas,at the inlet opening of the tube there exists the influx of momentumamounting to pQV dt since fluid having the mass of pQdt (0 being thevoluminal flowrate of the fluid) flows thereinto at the speed V and atthe outlet opening there exists the outflow of momentum amounting to pQVdt (V representing the flowing-out speed of fluid at the outlet openingB of the tube). Therefore, the increase of momentum of fluid within thetube in an infinitesimal time dt, amounts to pQ( VB V )dt.

With the above paragraphs (1) and 2) in which the forces working ontothe fluid in the tube and the increase of momentum of the fluid duringits passing through the tube in an infinitesimal time dt are obtainedand further in view of the law of conservation of momentum, followingequation is obtained:

Following equation of continuity is also established, since the fluid tobe measured by the present invention meter is incompressible fluid of asteady flow as described above.

This equation is solved for V and V as follows:

V and V in the aforementioned equation are substituted by the abovevalues, and the following equation is obtained:

The resultant of forces acting on the movable Venturi type tube is zero,when the tube stands still. Said resultant consists of the force fapplied to the tube by the fluid flowing therein, that is, the reactionforce of the aforementioned force f, the force I w resulting from thepressure exerted on members fitted to the tube at its opposite openends, gravity and an external force F working on the tube to keep it inbalance, said force F being, for example, the elasticity of the elasticjoints fitted to the tube.

Among those forces, the force I w is expressed in the followingequation, in which 8,,* and 8 represent ef fective areas of the membersfitted to the movable Venturi type tube at its inlet and outlet openingsand P represents the pressure outside of the Venturi tube.

Hence, the conditions of forces for balancing the movable Venturi typetube is established as follows, in which ug' represents the gravity ofmass .1..

f+ S *P S *P (S +S )P+(S +S )P+F +Ag it From the above equations (I) and(II), following equation is established:

When the elastic joints fitted to the tube are bellows, (S,,* S and(S,,* S in the above equation will be substituted by S, and S B whichcorrespond to each effective areas of the bellows.

Said equation (III) is a formulated working hypothesis of the presentflow meter.

In said equation (III), if S is equal S,,, the right side value of theequation becomes zero, to wit, the flowrate Q disappears from theequation, and consequently it is not possible to calculate said O.Hence, it is prerequisite that S is not equal to S Though either 8,, orS can be larger than the other, the description is made with referenceto examples in which S S The movable Venturi type may be of anyconfiguration provided that it has inlet and outlet openings ofdifferent sectional areas 8,, and S When 8,, is larger than S such typeof tube will resemble a Venturi tube in which the cross sectional areaof the tube gradually diminishes towards the outlet opening. The presentinvention meter can be placed in any direction, but it is mostpreferable to place it in a horizontal direction, because in thisinstance 3 becomes zero, so that the equation (III) will assume asimplified form as follows and so that the structure of the meter canalso be simplified.

a, (IV) The flowrate Q is obtainable from the above equation bymeasuring three factors, viz., (P P), (P P) and F. Said Q may beobtained by measuring only one or two of said three factors when themeter is modified in accordance with some of the following examples.

SUMMARY OF THE INVENTION It is an object of the present invention toprovide a flow meter, the construction of which is based on the aboveanalysis, and especially to the flow meter which will properly indicatethe rate of flow of a liquid passing therethrough regardless ofviscosity losses.

It is a further object of the present invention to provide for a flowmeter of the aforementioned type which is simple in construction andwhich will operate properly during extended use.

With these objects in view, the flow meter according to the presentinvention mainly comprises a Venturi tube having opposite ends ofdifferent cross sections and mounted movable in axial direction, meansfor admitting flowing liquid at one end and means for receiving theliquid after it has flowed through said Venturi tube at the other endthereof, first actuating means connected to the Venturi tube andactuated by and proportionately to movement of the same in axialdirection during flow of the liquid therethrough, second actuating meansactuated by the pressure in the liquid at the inlet and at the outletend of the movable Venturi tube, and means for determining the actualflow of liquid through the Venturi tube, which lastmentioned means areactuated by the first and second actuating means.

The novel features which are considered as characteristic for theinvention are set forth in particular in the appended claims. Theinvention itself, however, both as to its construction and its method ofoperation, together with additional objects and advantages thereof, willbe best understood from the following desctiption of specificembodiments when read in connection with the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING FIGS. 1 6 show embodiments of theinvention meter in diagrammatic cross section; and

FIGS. 7 9 schematically illustrate means connected to elements of thevarious embodiments shown in FIGS. 1-6 for indicating the flowrate ofthe liquid.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Common to all embodiments is atube 1 having an open end 2 of a comparatively large diameter S A and anopposite open end 3 of a comparatively small diameter S Either said openends with the diameter S A or S can be utilized as an inlet of liquid tobe measured by the meter. A pair of tubes 4,4 forming an inlet andoutlet of the liquid into the meter are fixed spaced from each othercoaxial with tube 1 and the latter is axially movable between facingends of the tube 4.

The Venturi type tube 1 is arranged between the tubes 4,4 and is movablyconnected to the latter by elastic joints or resilient means 7,8 such asbellows, springs and the like. A movable detecting rod 5 in form of amagnetic core is fitted at one end of its ends directly or indirectly tothe movable tube 1 and extends into a differential detecting means orcoil 6.

The elastic joints 7 and 8 are constituted in the embodiments shown inFIGS. 1, 2, 3 and 5, by closed tubular elastic bodies 12,12 or bellowswhich are fluidtightly extended between additional pressure-receivingannular members 9,10 having sectional areas 8 8 and beingcircumferentially provided about the openings 2,3 of the tube 1, andannular flanges 11,11 fited about the fixed tubes 4,4 adjacent to theiropen ends. In FIG. 4, one of elastic joints 7 is similar to those inFIGS. 1,2,3 and 5, while the other joint 8 consists of coil springsprovided between the opening 3 of the tube 1 and the fixed tube 4, whichpermit the flow of fluid past the springs into a sealed housing 17.

FIG. 1 illustrates a flow meter of the type in which flowrate Q isobtainable by measuring two values, i.e., the force F and the differenceof pressure (P A P The embodiment illustrated in FIG. 1, tubes 14,14respectively fitted to the flanges 11,11 of the fixed tubes 4,4 andopening into bellows 7,8 are connected by a pressure-difference gauge 16having a diaphragm 15. The difference of the pressure P and P atopenings 2 and 3 of the movable Venturi type tube is thus applied to andmeasured by said gauge. Since in this embodiment, the sectional areas SA and S',, of additional pressure receiving annular surfaces of themembers 9,10 are made equal, S,,, S,, and S in the equation (IV) becomeequal to establish the following equation.

1 1 (PFPB) +F= Q This equation solved for the flowrate follows: \/s' AE) +F The flowrate Q is thus obtainable from this equation (V) bymeasuring its F and (P P As a movable detecting rod 5 fixed at its oneend to the movable tube 1 displaces in accordance with the displacementof the tube 1, the value of displacement of the tube is measured by adifferential detecting means 6 and the force F which is proportioned tosaid value of displacement of the tube is obtainable. The difference ofpressure (P,, P is obtainable by the gauge 16, as above described.

FIG. 7 schematically indicates the means for determining the flowratefrom the above values. As shown in F IG. 7 a pair of transducers arerespectively connected to the diaphragm 15 of the pressure differencegauge 16 and to the coil 6 to produce signals corresponding to thedeflection of the diaphragm 15 and the current induced in the coil 6during movement of the core 5 relative thereto. The transducers arerespectively connected to a pair of indicators and a computer whichcalculates, in a known manner from the signals received, the flow rateof the liquid passing through the flow meter so that the flowrate may beread from the flow indicator connected to the computer.

A flow meter of the type in which flowrate Q is obtainable by measuringtwo values of difference of pressure, i.e., the difference of pressure(P,, P) and (P P) is illustrated in FIG. 2.

In the embodiment illustrated in FIG. 2, the movabletube 1, the elasticjoints 7,8, the movable detecting rod 5 and facing end portions of thefixed tubes 4,4 are all enclosed in a sealed housing 17, while the outerfree ends of the fixed tubes 4,4 open to the outside of the housing.Electrical value of the displacement of the movable Venturi type tube 1which is detected by the differential transformer 5,6 and amplified byan amplifier 18 operates a pressure regulating device 19 such as anelectrically actuated pump connected to the sealed housing 17 toregulate the pressure in the housing to thus reduce the displacement ofthe tube 1 to zero. Since the displacement of the tube 1 is maintainedat zero by regulating the pressure P at the outside of the tube 1 asabove-described, the external force for balancing the tube becomes zero.

The equation (IV) is, therefore, convertible as follows:

This equation is further solved for the flowrate Q to give the followingequation.

1 1 (eye; 6

From this equation, the flowrate Q is obtainable by measuring thedifference of pressure (P,, P) and (P P). The pressure differences (P P)and (P P) are measured by pressure difference measuring gauges 16,16provided at the outside of the sealed housing and each having twopressure chambers separated by a diaphragm 15, one of said chambers ofone gauge communicates with the interior of the bellows 7 through aconnecting tube 14, and one of the chambers of the other gaugecommunicates with the interior of the bellows 8 through a similarconnecting tube 14. The other chamber of each gauge communicates withthe interior of the sealed housing 17 through a tube 20. Since thepressure F at the outside of the movable tube 1 does not appear in theequation (VI) when S, is equal to S,,, and consequently the pressure Fcannot be ob-.

tained from the equation, it is prerequisite to construct the meter soas to have the S A which is not equal to S FIG. 8 schematicallyillustrates the means connected to the diaphragms 15 of the two pressuredifference gauges 16 of the embodiment illustrated in FIG. 2 fordetermining the flowrate. As shown in FIG. 8 a pair of transducers arerespectively connected to the two diaphragms to produce signalscorresponding to the deflection of the diaphragms and the transducersare connected over pressure difference indicators to a computer whichcalculates in a known manner from the signals received, the flowrate ofthe liquid passing through the flow meter so that the flowrate may beread from the flow indicator connected to the computer.

A meter of the type in which flowrate Q is obtainable by solelymeasuring a single value, i.e., the force F is illustrated in FIG. 3.

In the embodiment illustrated in FIG. 3, which is of most simpleconstruction, the flowrate Q of the fluid is obtained by simplymeasuring a single value of F which is the external force exerted on themovable tube 1. In this embodiment, a pair of connecting tubes 14,14communicate with one end respectively with the interior of the bellows 7or 8 and with the other end respectively with auxiliary bellows 7' or 8having an effective area equal to that of additional pressure-receivingsurfaces of the members 9,10. The free ends or the movable plates ofsaid auxiliary bellows 7',8' which oppose each other are connected tothe movable tube 1, i.e., respectively to the members 9 and 10 connectedto the opposite ends of tube 1.

In the meter of the above constructions, the force F working on themovable tube 1 may be expressed by the following equation, in which F isthe elasticity of the bellows 7,8 and 7',8'. Said value is proportionedto the displacement value of the tube 1.

The equation (IV) is, therefore, convertible as follows:

This equation is solved for Q to obtain the following The flowrate Q isthus obtainable by detecting through the differential transformer 5,6the F which is proportioned to the displacement value of the tube 1 asabove-described.

As shown in FIG. 9, the coil 6 is connected to a transducer whichproduces a signal corresponding to the current produced in the coil 6 inaccordance with the shifted position of the core relative thereto sothat the flowrate may be read on a flow indicator connected to thetransducer.

A meter of the type in which the flowrate Q is obtainable from twovalues is illustrated in FIG. 4.

In this embodiment illustrated in FIG. 4, the pressure at the outside ofthe tube 1 is made equal to P of P,,. For this purpose, a sealed housing17 encloses the tube 1, the joints 7,13, and the fixed tubes 4,4 whichare fluid-tightly fitted to the housing 17 and which extend beyondopposite ends of the housing. One of the joints 13 comprises a pluralityof springs arranged spaced from each other in the housing 17. By makingthe structures of the meter as illustrated in FIG. 4 in which one of thejoints 7 and the scaled housing 17 are connected by tubes 14 and 20 witha gauge 16 having a diaphragm 15 therebetween, the force P becomes equalto the force P The flowrate Q is thus obtainable by measuring (P P andthe external force F exerted onto the tube 1. The equation (IV) isconverted in this instance as follows:

Q: BA(PA PB)+F a V 3 S In'this embodiment, the arrangement asillustrated in (VIII) FIG. 7 is used for determining the flowrate of theliquid passing through the meter and the elements illustrated in FIG. 7are connected to each other and to the coil 6 and the diaphragm 15 asdescribed above in connection with the embodiment shown in FIG. 1.

The embodiments shown in FIGS. 1-4 comprise first and second actuatingmeans cooperating with means for determining the actual flow of liquidthrough the flow meter. The first actuating means in each embodimentcomprise a magnetic core 5 fixed to the venturi tube 1 for movementtherewith in axial direction and a coil 6 surrounding the core. Thesecond actuating means are actuated by the pressure of liquid at theinlet end and at the outlet end of the venturi tube and they areconstituted in the embodiments shown in FIGS. 1, 2 and 4 bypressure-differential gauges 15, 16 and in the embodiment of FIG. 3 byauxiliary bellow 7', 8'.

In the embodiments shown in FIGS. 1 and 4, the first and secondactuating means act directly on the means for determining flow ofliquid, whereas in the embodiment of FIG. 2, the first actuating means,and in the embodiment the second actuating means restrict movement ofthe venturi tube during change of flow of liquid and act thus indirectlyon the means for determining flow of liquid through the flow meter.

A meter of the type in which the flowrate Q is obtainable throughmeasuring a single value of the force F is illustrated in FIG. 5.

FIG. 5 illustrates an embodiment in which Bernouillis theorem holdstrue. When said theorem is applicable, following relation exists betweenthe difference of pressure P P and flowrate Q.

PPPFWQ (S g-s x) (1x When the equation (V) is rewritten in. view of theabove equation (IX) provided that S A S,, S', the following equation (X)is obtained.

The flowrate Q is, thus, obtainable by simply measuring said force F bythe core 5 connected to the Venturi tube 1 for movement therewith andthe coil 6 cooperating with the core. The means for detecting thedifference of pressure P,,, P illustrated in FIG. 1 is no longernecessary in this embodiment and eliminated therefrom.

In the embodiment illustrated in FIG. 6, the means for detecting thedifference of pressure P P are eliminated as in the embodiment of FIG.5, and the movable tube 1 and fixed tubes 4,4 are connected by elastictubes 7',8' such as bellows of diameters corresponding to those of themovable tube and fixed tubes. Contrary to other embodiments, the tube 1in this embodiment is not provided with additional pressure-receivingmembers such as the one indicated by numerals 9,10 in FIGS. 1 to 5. Asealed housing surrounds the tube 1, the joints 7' and 8 and the innerportions of the fixed tubes 4. In order to make the pressure in thesealed housing 17 equal to P one of the fixed tubes 4 is provided with apressure regulating portion 21 which is either a pore or a softmembrance. The flowrate is, thus, obtainable in this embodiment bydetecting the displacement value of the tube, by a differentialtransformer 5,6 of a construction as described above.

In the embodiments shown in FIGS. 5 and 6, the coil 5 of thedifferential transformer is connected to a transducer as shown in FIG. 9so that the flowrate may be read on the flow indicator connected to thetransducer.

It will be understood that each of the elements described above, or twoor more together, may also find a useful application in other types ofmovable Venturi type flow meters differing from the types describedabove.

While the invention has been illustrated and described as embodied in amovable Venturi type flow meter for correctly indicating the flowrateregardless of the viscosity of the liquid to be metered, it is notintended to be limited to the details shown, since various modificationsand structural changes may be made without departing in any way from thespirit of the present invention.

Without further analysis, the foregoing will so fully reveal the gist ofthe present invention that others can by applying current knowledgereadily adapt it for various applications without omitting featuresthat, from the standpoint of prior art, fairly constitute essentialcharacteristics of the generic or specific aspects of this inventionand, therefore, such adaptations should and 1 1 i re 3* are intended tobe comprehended within the meaning and range of equivalence of thefollow claims.

What is claimed as new and desired to be protected by Letters Patent isset forth in the appended l. A flow meter comprising a Venturi tubehaving opposite ends of different cross sections and being mountedmovable in an axial direction along a horizontal axis; first fixed meansfor supplying flowing liquid at one end and second fixed means forreceiving the liquid after it has flowed through said Venturi tube atthe other end thereof; first resilient means connecting said first fixedmeans to said one end of said Venturi tube and second resilient meansconnecting said other end to said second fixed means to bias saidVenturi tube to a neutral position in the absence of flow of liquid;first actuating means connected to said Venturi tube and actuated by andproportionately to movement of the same in said axial direction duringflow of said liquid therethrough; second actuating means actuated by thepressure of said liquid at said inlet and the pressure at said outletend of said Venturitube; and means for determining the actual flow ofliquid through said Venturi tube, said last-mentioned means beingresponsive to said first and second actuating means.

2. A flow meter as defined in claim 1, wherein said first fixed meansfor supplying liquid at one end and said second fixed means forreceiving the liquid at the other end of said Venturi tube comprise apair of stationary tubes aligned with and respectively arranged axiallyspaced from said opposite ends of said Venturi tube.

3. A flow meter as defined in claim 2, wherein said first actuatingmeans comprises a magnetic core connected to said Venturi tube formovement therewith in axial direction and a stationary coil surroundingsaid core.

4. A flow meter as defined in claim 3, wherein said resilient meanscomprise a pair of bellows respectively forming a pair of chambers aboutsaid opposite open ends of said Venturi tube and the adjacent ends ofsaid stationary tubes, and wherein said second actuating means comprisepressure difference gauge means including diaphragm means and passagemeans leading from said chambers to opposite sides of said diaphragmmeans so as to deflect the latter in dependence on the difference of thepressure of the liquid at said opposite ends of said Venturi tube.

5. A flow meter as defined in claim 4, wherein said means fordetermining actual flow of liquid through said Venturi tube comprise apair of transducer means connected to said diaphragm means and saidstationary coil, respectively, and computer means connected to saidtransducer means.

6. A flow meter as defined in claim 4, and including a fluid-tighthousing surrounding said Venturi tube and said bellows connectedthereto, means connected to said first actuating means for regulatingthe pressure in said housing so as to maintain said Venturi tube in saidneutral position, said second actuating means comprising a pair ofpressure difference gauge means, each including a diaphragm, and passagemeans for transmitting the fluid pressure in one of said chambers andthat in the interior of said housing respectively to opposite sides ofone of said diaphragms and the fluid pressure in the other of saidchambersand that in the interior of said housing respectively toopposite sides of the other said diaphragms.

7. A flow meter as defined in claim 6, wherein said means fordetermining actual flow of liquid through said Venturi tube comprises apair of transducer means respectively connected to the diaphragms ofsaid pair of pressure difference gauge means and computer meansconnected to said transducer means.

8. A flow meter as defined in claim 6, and including radially outwardlyextending pressure receiving members fixed to and surrounding said openends of said Venturi tube, said pair of bellows being respectively fixedto the outer peripheries of said pressure receiving members so that oneside of each pressure receiving member is subjected to the pressure ofthe liquid in the respective chamber and the other side to the pressureof the liquid in said housing.

9. A flow meter as defined in claim 4 and including radially outwardlyextending pressure receiving members fixed to and surrounding said openends of said Venturi tube, said pair of bellows being respectively fixedto the outer peripheries of said pressure receiving members so that thelatter are subjected to the pressure of the liquid in said chambers.

10. A flow meter as defined in claim 9, wherein said radially outwardlyextending pressure receiving members are annular membershaving equalouter diame- 'ters.

11. A flow meter as defined in claim 3, wherein said resilient meanscomprises a bellows forming a chamber about one of said opposite openends of the Venturi tube and the adjacent end of the corresponding oneof said stationary tube so as to form a chamber about said adjacentends, and spring means between the other end of said Venturi tube andthe adjacent end of the other of said stationary tubes, and including afluid-tight housing surrounding said Venturi tubes and said resilientmeans, said spring means being arranged so that the space between saidother end of said Venturi tube and said adjacent end of the otherstationary tube communicates with the interior of said housing wherebythe latter will be filled with liquid passing through the Venturi tube,and the liquid in the housing will be maintained at a pressure equal tothe pressure at said other end of said Venturi tube, said secondactuating means comprising difference gauge means including a diaphragmand passage means for transmitting the pressure of the liquid in saidchamber and in the interior of said housing respectively to oppositesides of said diaphragm.

12. A flow meter as defined in claim 11, wherein said means fordetecting actual flow of liquid through said Venturi tube comprises apair of transducer means respectively connected to said diaphragm andsaid coil, and computer means connected to said transducer means.

13. A flow meter as defined in claim 3, and including radially outwardlyextending pressure receiving members fixed to and surrounding said openends of said Venturi tube, said resilient means comprise a pair ofbellows respectively connected to the outer peripheries of said pressurereceiving members and forming a pair of chambers about said oppositeends of said Venturi tube and the adjacent ends of said stationarytubes, and wherein said second actuating means comprise a pair of saidmembers.

14. A flow meter as defined in claim 13, wherein said means fordetecting actual flow of liquid through said Venturi tube comprisestransducer means connected to said stationary coil and flow indicatormeans connected to said transducer means.

0 ll k i i

1. A flow meter comprising a Venturi tube having opposite ends ofdifferent cross sections and being mounted movable in an axial directionalong a horizontal axis; first fixed means for supplying flowing liquidat one end and second fixed means for receiving the liquid after it hasflowed through said Venturi tube at the other end thereof; firstresilient means connecting said first fixed means to said one end ofsaid Venturi tube and second resilient means connecting said other endto said second fixed means to bias said Venturi tube to a neutralposition in tHe absence of flow of liquid; first actuating meansconnected to said Venturi tube and actuated by and proportionately tomovement of the same in said axial direction during flow of said liquidtherethrough; second actuating means actuated by the pressure of saidliquid at said inlet and the pressure at said outlet end of said Venturitube; and means for determining the actual flow of liquid through saidVenturi tube, said last-mentioned means being responsive to said firstand second actuating means.
 2. A flow meter as defined in claim 1,wherein said first fixed means for supplying liquid at one end and saidsecond fixed means for receiving the liquid at the other end of saidVenturi tube comprise a pair of stationary tubes aligned with andrespectively arranged axially spaced from said opposite ends of saidVenturi tube.
 3. A flow meter as defined in claim 2, wherein said firstactuating means comprises a magnetic core connected to said Venturi tubefor movement therewith in axial direction and a stationary coilsurrounding said core.
 4. A flow meter as defined in claim 3, whereinsaid resilient means comprise a pair of bellows respectively forming apair of chambers about said opposite open ends of said Venturi tube andthe adjacent ends of said stationary tubes, and wherein said secondactuating means comprise pressure difference gauge means includingdiaphragm means and passage means leading from said chambers to oppositesides of said diaphragm means so as to deflect the latter in dependenceon the difference of the pressure of the liquid at said opposite ends ofsaid Venturi tube.
 5. A flow meter as defined in claim 4, wherein saidmeans for determining actual flow of liquid through said Venturi tubecomprise a pair of transducer means connected to said diaphragm meansand said stationary coil, respectively, and computer means connected tosaid transducer means.
 6. A flow meter as defined in claim 4, andincluding a fluid-tight housing surrounding said Venturi tube and saidbellows connected thereto, means connected to said first actuating meansfor regulating the pressure in said housing so as to maintain saidVenturi tube in said neutral position, said second actuating meanscomprising a pair of pressure difference gauge means, each including adiaphragm, and passage means for transmitting the fluid pressure in oneof said chambers and that in the interior of said housing respectivelyto opposite sides of one of said diaphragms and the fluid pressure inthe other of said chambers and that in the interior of said housingrespectively to opposite sides of the other said diaphragms.
 7. A flowmeter as defined in claim 6, wherein said means for determining actualflow of liquid through said Venturi tube comprises a pair of transducermeans respectively connected to the diaphragms of said pair of pressuredifference gauge means and computer means connected to said transducermeans.
 8. A flow meter as defined in claim 6, and including radiallyoutwardly extending pressure receiving members fixed to and surroundingsaid open ends of said Venturi tube, said pair of bellows beingrespectively fixed to the outer peripheries of said pressure receivingmembers so that one side of each pressure receiving member is subjectedto the pressure of the liquid in the respective chamber and the otherside to the pressure of the liquid in said housing.
 9. A flow meter asdefined in claim 4 and including radially outwardly extending pressurereceiving members fixed to and surrounding said open ends of saidVenturi tube, said pair of bellows being respectively fixed to the outerperipheries of said pressure receiving members so that the latter aresubjected to the pressure of the liquid in said chambers.
 10. A flowmeter as defined in claim 9, wherein said radially outwardly extendingpressure receiving members are annular members having equal outerdiameters.
 11. A flow meter as defined in claim 3, wherein saidresilient meAns comprises a bellows forming a chamber about one of saidopposite open ends of the Venturi tube and the adjacent end of thecorresponding one of said stationary tube so as to form a chamber aboutsaid adjacent ends, and spring means between the other end of saidVenturi tube and the adjacent end of the other of said stationary tubes,and including a fluid-tight housing surrounding said Venturi tubes andsaid resilient means, said spring means being arranged so that the spacebetween said other end of said Venturi tube and said adjacent end of theother stationary tube communicates with the interior of said housingwhereby the latter will be filled with liquid passing through theVenturi tube, and the liquid in the housing will be maintained at apressure equal to the pressure at said other end of said Venturi tube,said second actuating means comprising difference gauge means includinga diaphragm and passage means for transmitting the pressure of theliquid in said chamber and in the interior of said housing respectivelyto opposite sides of said diaphragm.
 12. A flow meter as defined inclaim 11, wherein said means for detecting actual flow of liquid throughsaid Venturi tube comprises a pair of transducer means respectivelyconnected to said diaphragm and said coil, and computer means connectedto said transducer means.
 13. A flow meter as defined in claim 3, andincluding radially outwardly extending pressure receiving members fixedto and surrounding said open ends of said Venturi tube, said resilientmeans comprise a pair of bellows respectively connected to the outerperipheries of said pressure receiving members and forming a pair ofchambers about said opposite ends of said Venturi tube and the adjacentends of said stationary tubes, and wherein said second actuating meanscomprise a pair of additional bellow means each including a movableplate and a stationary plate, and a pair of passage means respectivelyproviding communication between the interior of said pair of chambersand the interior of said pair of additional bellows, the movable platesof said pair of additional bellows being respectively fixed to saidpressure receiving members and having respectively effective pressurereceiving areas equal to that of said members.
 14. A flow meter asdefined in claim 13, wherein said means for detecting actual flow ofliquid through said Venturi tube comprises transducer means connected tosaid stationary coil and flow indicator means connected to saidtransducer means.